This invention relates to an electronic musical instrument constructing tone waveforms by sequentially aligning wave samples in which a sampling frequency is harmonized with the tone frequency.
In an electronic musical instrument of a digital processing type, a tone waveform is formed by sequentially aligning amplitude samples of a tone waveform at a constant sampling interval. The following two systems have heretofore been practiced as the musical tone forming system by sampling (aligning samples): One is to perform sampling with a constant sampling frequency regardless of the frequency of a tone to be formed and the other is to have the sampling frequency synchronized with the frequency of the tone to be formed. In the former system the ratio between the tone frequency and the sampling frequency is generally non-integer and therefor an aliasing noise which is not harmonized with the tone frequency is produced as will be apparent from the sampling theory. For this reason, this system requires a device for reducing the aliasing noise and the musical instrument as a whole becomes larger. On the other hand, this system has the advantage that a time sharing operation can be realized owing to the constant sampling frequency, i.e., a single system of the apparatus can be used on a time shared basis for sampling a plurality of tone waveforms of different pitches and the device for forming tones thereby can be economized. In the latter system, the tone frequency is harmonized with the sampling frequency and, accordingly, frequency-reflected components are also harmonized with the tone frequency and no aliasing noise is produced. The latter system therefore has the advantage that no particular device is necessary for reducing the aliasing noise. Since, however, different sampling frequencies must be used for tones of different pitches, the latter system is incapable of forming tones by the time sharing operation. The latter system therefore requires parallel provision of a plurality of tone forming systems in the same number as a maximum number of tones to be produced simultaneously and this necessitates an apparatus of a large scale.